Surface layer materials are often imaged or patterned for many utilitarian purposes. The surface layers may include vacuum deposited thin films, solution coatings, and electroless or electroplated films. Patterned conductive surface layers may find use in both passive and active electronic circuits, display components, antennas for radio frequency identification tags (RFID), wireless local area networks (LAN), and proximity detectors as well as antennas for communication such as pagers, cell phones, and satellite reception. Optical surface layers may find application as optical components such as diffractive optical elements and security images, or in telecommunication applications as components that can perform optical switching, modulation, and multiplexing or demultiplexing.
There are techniques for forming patterns in surface layers. Two useful methods are chemical etching and laser ablation. Images or patterns created by chemical etching are formed by selectively dissolving the surface layer with the appropriate chemicals or by energy ablation are formed by explosively detaching and removing a thin surface layer in a selective manner to create an image or pattern. However, each of these methods has limitations.
Chemical etching is a multiple step process that may create hazardous waste. Typically a chemical or photo-resist is applied to selected parts of a surface that is to be patterned or imaged. Then, a chemical is applied on the entire surface and is able to remove the coating (e.g. copper) exposed on the surface but not the coating on the part of surface covered by the chemical or photo-resist. The chemical solution containing the dissolved surface layer material is then washed off of the imaged article. The often hazardous solution is collected and treated in a safe manner at some expense. This method is undesirable due to the multiple process steps and the imaged article can have residual photo-resist residue and undercut sidewalls of the image.
Contemporary methods of utilizing lasers to pattern or micro-machine materials rely on the physical phenomena of ablation. Energy ablation is a simpler process that does not involve hazardous waste disposal. Typically, the surface layer of an article to be imaged is exposed (for example through a mask) with light pulses from a high-energy source, such as a laser or a flash lamp. These pulses of energy are absorbed by parts of the surface layer not covered by the mask, and the energy impacting the layer causes a sudden increase in surface temperature for a short time. The rapid rise in temperature causes the surface layer material to explosively detach or eject from the substrate and create a pattern corresponding to the mask pattern.